The present invention relates to a thermoplastic resin composition having excellent long-term heat-aging properties. More particularly, it relates to a thermoplastic resin composition having excellent impact resistance, heat resistance, chemical resistance and weather resistance, and further remarkably improved in long-term heat-aging properties.
Polycarbonate (PC) resins have excellent heat resistance and mechanical properties, the molded products thereof are excessively reduced in impact strength when they are flawed because of high notch sensitivity. PC resins also have a disadvantage that it is necessitated to set the molding temperature in a high range due to too high heat resistance, so that they are inexpedient for molding of large-sized articles.
On the other hand, ABS resins (acrylonitrile-butadiene-styrene resins) are a material having a good balance of properties such as moldability, impact strength and dimensional stability, and widely used for a variety of commercial products such as automobiles, domestic electrical appliances, OA machines, etc., but they have a disadvantage that they are low in heat resistance. Japanese Patent Publication (KOKOKU) No. 38-15225 proposes blending of a PC resin with an ABS resin having good compatibility with the PC resin to thereby improve such properties as notched impact strength, molding workability and heat resistance. The PC resin/ABS resin polymer alloys (which may hereinafter be referred to as "PC/ABS polyblends") are now one of the typical resin compositions popularly used in the fields of OA machines, vehicles and such.
Another drawback to the ABS resins is poor weather resistance due to use of butadiene rubber. Japanese Patent Publication (KOKOKU) No. 51-24540 proposes polyblending of a PC resin and an AES resin using ethylene-propylene (EP) rubber to improve stain resistance. Japanese Patent Publication (KOKOKU) No. 1-57699 proposes addition of a specific plasticizer to the PC resin/AES resin polymer alloys (which may hereinafter be referred to as "PC/AES polyblends") to improve weld strength. Further, Japanese Patent Publication KOKOKU) No. 3-40064 proposes optimization of the rubber content, graft ratio and molecular weight of the PC/AES polyblends to improve weld appearance and coating properties. Japanese Patent Publication (KOKOKU) No. 1-17501 proposes polyblending of the three types of resin, i.e. PC resin, ABS resin and AES resin, to improve low-temperature impact strength, weld strength and color development. Japanese Patent Publication (KOKOKU) No. 4-29696 proposes addition of .alpha.-alkylstyrene as the graft resin component of the PC/AES polyblends to improve thermal decomposability in the course of granulation and molding work. Japanese Patent Publication (KOKOKU) No. 4-56063 proposes optimization of melt viscosity of the AES resin in the PC/AES polyblends to improve weld strength. Japanese Patent Publication (KOKOKU) No. 5-79699 proposes optimization of the rubber content of the PC/AES polyblends to improve low-temperature impact strength.
As viewed above, since the PC/ABS and PC/AES polyblends have excellent properties, various use for them are found. But when these resins once molded into a product are exposed to high temperatures for a long time in a practical use environment, their properties are deteriorated drastically. This is attributable to such causes as deterioration of the PC resin, deterioration of the grafted or ungrafted resin and deterioration of the rubber, but no proposal of the attempt for solving these problems has ever been made in the past.
As a result of the present inventors' earnest studies to solve the above problems, it has been found that a thermoplastic resin composition comprising a specific rubber-modified thermoplastic resin, a specific thermoplastic resin, a polycarbonate resin and a heat-aging resistor, with the content of vinyl cyanide compound in the whole composition being defined, has excellent long-term heat-aging properties.
The present invention has been attained on the basis of the above finding.